In the field of medical technology, a large number of apparatuses are known for delivering fluids to a patient or removing fluids from a patient via a hose line. The access to the patient generally takes place with a catheter for introduction into body organs, or a cannula or needle for puncturing vessels. During the examination or treatment, correct access to the patient must be ensured. It is therefore necessary to monitor the patient access.
In extracorporeal blood treatment, there are particularly high demands on reliability of the vascular access In extracorporeal blood treatment, blood is removed from the patient via an arterial hose line that has an arterial puncture cannula, passed through a dialyzer, and delivered back to the patient via a venous blood line that has a venous puncture cannula. Despite regular monitoring of the patient access by hospital staff, there is the risk of the venous puncture cannula slipping out of the patient's blood vessel unnoticed. When the arterial cannula slips out of the patient's artery, air is sucked into the arterial hose line, which leads to a visual and/or optical alarm and to interruption of the treatment on account of air being detected on the machine side. However, when the venous cannula slips out of the patient's vein, blood can freely flow into the surroundings without being readily detected. If the venous cannula slips out and is not detected immediately, the patient could bleed to death.
To solve this problem, many different devices are known. Some of these devices rely on safety devices provided as standard in blood treatment machines and trigger an immediate interruption of the extracorporeal blood circuit in the event of an incorrect vascular access. The safety devices provided as standard in treatment machines are generally based on monitoring the pressure in the extracorporeal blood circuit. In practice, however, it has been shown that the slipping-out of the venous puncture cannula cannot be detected with sufficient reliability solely by monitoring the pressure in the extracorporeal blood circuit. Some known safety devices do have adequate sensitivity, but are overly sensitive to changes in the patient's position, and this often leads to false alarms. Existing blood treatment apparatuses also cannot be readily retrofitted with the known monitoring devices, but rather the retrofitting is an expensive and cost-intensive intervention.
DE 44 32 348 C2 describes a safety device for a hose line conveying blood, wound discharge or infusion, said safety device reacting to a relative change in position of the hose line. The safety device of DE 44 32 348 C2 has a magnet that is fixed to the hose line and a reed contact that is fixed to the patient. If the hose line is tugged, the distance between the magnet and the reed contact changes and an alarm is triggered.
DE 199 53 068 A1 describes a mechanical safety device that can be fixed to the blood line of a dialysis machine. The safety device of DE 199 53 068 has elastically pre-tensioned clamping jaws, which can be held open by a locking bar fixed to the patient's body, and the blood line is placed between the clamping jaws. A change in position of the blood line moves the locking bar, causing the clamping jaws to pinch off the blood line. This leads to a pressure increase in the blood line, which is detected by the standard known devices for monitoring the pressure in dialysis apparatuses. However, fixing the mechanical safety device to the blood line and to the patient is complicated. Additionally, since the clamping jaws pinch off the blood line abruptly, it is not possible to trigger an alarm before the blood treatment is interrupted. Furthermore, the use of inexpensive plastics as a material for factory assembly of the blood line is also problematic due to the creep processes. The clamping jaws should not be under permanent pre-tensioning, but this is only the case when the clamping jaws are closed. However, since the blood line is pinched off when the clamping jaws are closed, the clamping jaws must be under pre-tensioning. If the device is produced from inexpensive plastics, this could lead to a permanent reduction in the pre-tensioning of the clamping jaws and thus to unfitness of the device for use, as a result of the creep process even at room temperature.